| My Z has pretty much been neglected for the past several months due to the overwhelming volume of work we went through with all of the 2.5" piping and MASSIVE SMIC groupbuy kits but have finally been able to get a breath of air. Last week I put some new shoes on the Z - BFG g-force TA KDs, which are some really excellent tires for the money - first gear has always been a matter of pedaling through the wheelspin as well as 2nd gear just the same. These tires, once you've given them a good spin to clean and warm them up, will pretty much plant second gear to the ground. :) I made a trip to Gainesville over the weekend to spend some much needed time with the family and on the way back when I boosted up to pass a slow driver, I heard the awful sound of exhaust pressure leaking from the driver's side of the engine bay. I pulled over at the next gas station to do a visual and after a few moments of looking and listening, I determined it was the driver's side manifold - somewhere at the back but I couldn't see any visual cracks. Most of you will recall these, but here's a pic of the manifolds: 
I put the car up and started taking things apart to drop the turbo and manifold. Got everything disassembled and the manifold off in just a couple of hours - noted that the two rear manifold nuts weren't tight like the others. One of the first things I noticed was a lot of carbon on the manifold flange around the rear #6 cylinder port. I pulled the gasket off the head to find this: 
When I built the manifolds, one design idea I wanted to test was to cut the manifold-head flange to allow the pipes to thermally expand/contract. This isn't seen in the images above as I didn't cut them until literally the last moment before they were installed, but the flange was cut between each port. The OEM gasket material is very slick and will allow for the flanges to creep so long as the fastening nuts aren't so tight to prevent this. By allowing the flanges to creep, the pipes will be able to actually expand and contract freely so as to prevent metal fatigue from taking over and creating cracks at the pipe to flange weld interface as had been seen in other manifolds. With this idea in mind, I only torqued the two rear nuts down to OE spec and left the other four nuts for the front and center flanges a bit looser. What is strange is that the two rear nuts on my manifold had actually loosened up and the other four were still nice and snug. This caused the breach of the rear gasket, obviously. The red arrow in the image is pointing to an area where the gasket material had completely seperated and blew out from the gasket substrate. The beast has 24,797 miles on this buildup as she sits. If you take a look at the pics above, you will see that there are differences in the assembly of each with respect to the welds at the pipe to flange interface. I did this intentionally to test the longevity of the different assembly techniques that were being discussed at the time. I was surprised that a leak developed on the driver's manifold given that it is the one with the reinforcing gussets and welded both inside and outside of the pipe where it meets the flange. Granted, the manifold wasn't the source of the leak here, but the passenger side manifold, without the extra weld and supporting gussets, is still totally leak-free. :) About four hours after tearing into her, she's back together, leak-free. :) Just thought I would share my experience with these one-off stainless steel tubular exhaust manifolds that many others, as well as myself, never predicted would last anywhere close to what they have.... For those interested, here's the buildup posts I made when I was constructing these manis:
[ http://twinturbo.net/net/viewmsg.aspx?forum=general&msg_id=1502300 ]
[ http://twinturbo.net/net/viewmsg.aspx?forum=general&msg_id=1500124 ] [ http://twinturbo.net/net/viewmsg.aspx?forum=general&msg_id=1487227 ] [ http://twinturbo.net/net/viewmsg.aspx?forum=general&msg_id=1492440 ] [ http://twinturbo.net/net/viewmsg.aspx?forum=general&msg_id=1500124 ] [ http://twinturbo.net/net/viewmsg.aspx?forum=general&msg_id=1498266 ]
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[ agpowers@bellsouth.net ] Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the tailor.
Albert Einstein
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AshsZ-II Ultimate Street Z - Exhaust Manifold Followup >>> - 
00:00:41 04/22/08
